Richard A. Lawrence
Other affiliations: University of Texas Health Science Center at San Antonio
Bio: Richard A. Lawrence is an academic researcher from United States Department of Veterans Affairs. The author has contributed to research in topics: Selenium deficiency & Selenium. The author has an hindex of 3, co-authored 3 publications receiving 3342 citations. Previous affiliations of Richard A. Lawrence include University of Texas Health Science Center at San Antonio.
TL;DR: Two peaks of glutathione peroxidase activity were present in the Sephadex G-150 gel filtration chromatogram of rat liver supernatant when 1.5 mM cumene hydroperoxide was used as substrate, and the second peak represents a second glutathienase activity which catalyzes the destruction of organic hydroperoxides but has little activity toward H 2 O 2 and which persists in severe selenium deficiency.
Abstract: Glutathione peroxidase activity in the liver supernatant from rats fed a Se-deficient diet for 2 weeks was 8% of control when measured with H 2 O 2 but 42% of control when assayed with cumene hydroperoxide. Two peaks of glutathione peroxidase activity were present in the Sephadex G-150 gel filtration chromatogram of rat liver supernatant when 1.5 mM cumene hydroperoxide was used as substrate. Only the first peak was detected when 0.25 mM H 2 O 2 was used as substrate. The first peak was absent from chromatograms of Se-deficient rat liver supernatants; but the second peak, which eluted at a position corresponding to M.W. = 39,000, appeared unchanged. The second peak thus represents a second glutathione peroxidase activity which catalyzes the destruction of organic hydroperoxides but has little activity toward H 2 O 2 and which persists in severe selenium deficiency.
TL;DR: The findings suggest that paraquat and diquat exert their acute toxicity largely through lipid peroxidation in selenium-deficient rats, and suggests that a seenium-dependent factor in addition to glutathione peroxidase exists that protects against lipidperoxidation.
Abstract: Paraquat and diquat facilitate formation of superoxide anion in biological systems, and lipid peroxidation has been postulated to be their mechanism of toxicity. Paraquat has been shown to be more toxic to selenium-deficient mice than to controls, presumably as the result of decreased activity of the selenoenzyme glutathione peroxidase. The present study was designed to measure lipid peroxidation and to assess toxicity in control and selenium-deficient rats given paraquat and diquat. Lipid peroxidation was measured by determining ethane production rates of intact animals; toxicity was assessed by survival and by histological and serum enzyme evidence of liver and kidney necrosis. Paraquat and diquat were both much more toxic to selenium-deficient rats than to control rats. Diquat (19.5 mumol/kg) caused rapid and massive liver and kidney necrosis and very high ethane production rates in selenium-deficient rats. The effect of paraquat (78 mumol/kg) was similar to that of diquat but was not as severe. Acutely lethal doses of paraquat (390 mumol/kg) and diquat (230 mumol/kg) in control rats caused very little ethane production and no evidence of liver necrosis. These findings suggest that paraquat and diquat exert their acute toxicity largely through lipid peroxidation in selenium-deficient rats. Selenium deficiency had no effect on superoxide dismutase activity in erythrocytes or in 105,000 g supernate of liver or kidney. Glutathione peroxidase, which represents the only well-characterized biochemical function of selenium in animals, was dissociated from the protective effect of selenium against diquat-induced lipid peroxidation and toxicity by a time-course study in which selenium-deficient rats were injected with 50 mug of selenium and later given diquat (19.5 mumol/kg). Within 10 h, the selenium injection provided significant protection against diquat-induced lipid peroxidation and mortality even though this treatment resulted in no rise in glutathione peroxidase activity of liver, kidney, lung, or plasma at 10 h. This suggests that a selenium-dependent factor in addition to glutathione peroxidase exists that protects against lipid peroxidation.
TL;DR: This chapter presents a procedure for the preparation of glutathione peroxidase, which is regarded as a major protective system against endogenously and exogenously induced lipid peroxidation.
Abstract: Publisher Summary This chapter presents a procedure for the preparation of glutathione peroxidase, which is regarded as a major protective system against endogenously and exogenously induced lipid peroxidation. Two types of methods are used for determining the activity of glutathione peroxidase. One involves a direct measurement of unconsumed glutathione (GSH) at fixed time periods by polarographic GSH analysis' (Method 1), or by the dithionitrobenzoic acid method (Method 2). The second approach takes advantage of the capability of glutathione reductase, with nicotinamide adenine dinucleotide phosphate (NADPH), to regenerate GSH from oxidized GSH. The decrease in NADPH is continuously measured spectrophotometrically, while the GSH concentration in the enzymatic cycle remains essentially constant (Method 3). A convenient source for the preparation of glutathione peroxidase is bovine blood including the following steps: hemolysate; organic solvent precipitation; phosphate precipitation; absorption to phenyl-sepharose; and washing on diethylaminoethyl (DEAE)–sephadex, S-300 sephacryl, and hydroxylapatite column.
TL;DR: The existing evidence support the view that oxidative stress may play a crucial role in cardiac and vascular abnormalities in different types of cardiovascular diseases and that the antioxidant therapy may prove beneficial in combating these problems.
Abstract: ObjectivesIn view of the critical role of intracellular Ca2+-overload in the genesis of myocyte dysfunction and the ability of reactive oxygen species (ROS) to induce the intracellular Ca2+-overload, this article is concerned with analysis of the existing literature with respect to the role of oxida
TL;DR: Current evidence in clinical research does not show unequivocal distinction between causal or associative relationships of pro-oxidants to the disease process.
Abstract: The occurrence of reactive oxygen species, known as pro-oxidants, is an attribute of normal aerobic life The steady-state formation of pro-oxidants is balanced by a similar rate of their consumption by antioxidants that are enzymatic and/or nonenzymatic "Oxidative stress" results from imbalance in this pro-oxidant-antioxidant equilibrium in favor of the pro-oxidants A number of diseases are associated with oxidative stress, being the basis of antioxidant therapy Current evidence in clinical research does not show unequivocal distinction between causal or associative relationships of pro-oxidants to the disease process
TL;DR: Diverse biological processes such as inflammation, carcinogenesis, ageing, radiation damage and photobiological effects appear to involve reactive oxygen species, and oxidative stress denotes a shift in the prooxidant/antioxidant balance in favor of the former.
Abstract: As a normal attribute of aerobic life, structural damage to organic compounds of a wide variety (DNA, proteins, carbohydrates and lipids) may occur as a consequence of oxidative reactions. Oxidative damage inflicted by reactive oxygen species has been called “oxidative stress”. Biological systems contain powerful enzymatic and nonenzymatic antioxidant systems, and oxidative stress denotes a shift in the prooxidant/antioxidant balance in favor of the former. Diverse biological processes such as inflammation, carcinogenesis, ageing, radiation damage and photobiological effects appear to involve reactive oxygen species. This field of research provides new perspectives in biochemical pharmacology, toxicology, radiation biochemistry as well as pathophysiology.
TL;DR: The present results indicate that a knock-out of GSHPx may be adequately compensated under nonstressed conditions, but that after administration of mitochondrial toxins GSHpx plays an important role in detoxifying increases in oxygen radicals.
Abstract: Glutathione peroxidase (GSHPx) is a critical intracellular enzyme involved in detoxification of hydrogen peroxide (H 2 O 2 ) to water. In the present study we examined the susceptibility of mice with a disruption of the glutathione peroxidase gene to the neurotoxic effects of malonate, 3-nitropropionic acid (3-NP), and 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP). Glutathione peroxidase knock-out mice showed no evidence of neuropathological or behavioral abnormalities at 2–3 months of age. Intrastriatal injections of malonate resulted in a significant twofold increase in lesion volume in homozygote GSHPx knock-out mice as compared to both heterozygote GSHPx knock-out and wild-type control mice. Malonate-induced increases in conversion of salicylate to 2,3- and 2,5-dihydroxybenzoic acid, an index of hydroxyl radical generation, were greater in homozygote GSHPx knock-out mice as compared with both heterozygote GSHPx knock-out and wild-type control mice. Administration of MPTP resulted in significantly greater depletions of dopamine, 3,4-dihydroxybenzoic acid, and homovanillic acid in GSHPx knock-out mice than those seen in wild-type control mice. Striatal 3-nitrotyrosine (3-NT) concentrations after MPTP were significantly increased in GSHPx knock-out mice as compared with wild-type control mice. Systemic 3-NP administration resulted in significantly greater striatal damage and increases in 3-NT in GSHPx knock-out mice as compared to wild-type control mice. The present results indicate that a knock-out of GSHPx may be adequately compensated under nonstressed conditions, but that after administration of mitochondrial toxins GSHPx plays an important role in detoxifying increases in oxygen radicals.